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(NoModeL) 2 Sheets-Sheet L E. THOMSON.

ELECTRIC MEASURING INSTRUMENT. 7

No. 413,292. s r Patented Oct. 22, 1889.-

WITNESSES: INVENTO/i' (No' Model.)

" E. THOMSON. ELECTRIC MEASURING INSTRUMENT. No. 413,292. Patented .0011. 22, 1889.

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UNITED; STATES PAT NT OFFICE.

ELIHIT THOMSON, OF LYNN, MAssACHUsETTs, ASSIGNOR To THE TI- oMsoN- noUsToN ELECTRIC COMPANY, OF CONNECTICUT.

ELECTRIC MEASURING-INSTRUMENT.

SPECIFICATION forming part of Letters Patent No. 413,292, dated October 22, 1889.

Application filed April 28, 1387. Serial No. 236,889 (No model.)

T 0% whom it may concern: her of breaks might be still further increased,

Be it known that I, ELIHU THOMSON, a citithe mass of iron or armature, arranged, as dezen of the United States, and a resident of scribed, toeiiect the variable closure of the Lynn, in the county of Essex and State of magnetic circuit around the conductor atall Massachusetts, have invented certain new portions of the range of movement of the and useful Electrical lVIeasuring-Instruments, apparatus, being properly mounted upon the of which the following is a specification. end of an arm fixed or pivoted according to My invention relates primarily to the electhe specified construction, so that there is a tro-magnet which is used for giving motion bodily movement ofthe mass or armature I0 to the index, pointer, recording-pencil, or when the conductor is stationary and the I marker, or other equivalent portion of the armature is movable. Ipreferto useamassof device; and it consists in the combination, iron of general U form mounted to move with an electric conductor, of a mass of iron bodily in a line such that the two sides or constantly and through its entire range of legs of the U will gradually move down over T5 movement forming a partial magnetic cirthe conductor to either side thereof. cuit around-the conduct-or, the movement of a My invention consists also in certain dewhich mass, or of the conductor, one or both, tails of construction and improved combinain the general longitudinal direction of the tions of parts, which will be first describedin conduct-or, under the influence of the current connection with the accompanying drawing 20 in the conductor, produces achange in the deand then specified in the claims. 7o gree of closure of the magnetic circuit around In the accompanying drawings, F1gure 1 is the conductor by the iron mass. a side elevation of an apparatus embodying In carrying out my invention the mass of my invention and properly constructed to iniron only may move with relation to the condicate the passage of very heavy electric our- 2 5 ductor or the conductor move with relation rents and their amount. Fig. 2 is a vertical to the iron, or both may move with relation section of the same apparatus on the line a a to one another, or both may move together, as of Fig. 1. Figs. 3, 4, and 5 are cross-sections will hereinafter appear. through the electric conductor and illustrate WVhile, therefore, in my claim at the end of the action of the device. .Figs. 6 and 7 illus- 3 this specification Lclaim a movable iron tratein cross-section modifications inthe form mass arranged, as described, to partially close of the electric conductor. Fig. 8 is a side elethe magnetic circuit around the conductor in vation of another form of electric conductor its normal position, I wish to be distinctly adapted to some of the purposes of my inunderstood as including by said claims the vention. Fig. 9 is a side elevation of a con- 35 converse cases and modifications just speciductor made as a coil, and FigrlO is a crossfied, some of the forms of which are hereinsection of the same. Fig. 11 illustrates the after described. preferred form of the coil or conductor. Figs.

The mass of iron which partially closes the 12, 13, 14, and 15 illustrate modifications magnetic circuit or field around the conductadapted to measuring differences of potential.

4 or is preferably of U form, the conductor Fig. 16 shows in side elevation, and Fig. 17 being included between the two legs of the in edge view, a form of the iron mass or U- U, and the field around the same magneticshaped armature which I prefer to employ. ally closed across the open ends of the legs. Figs. 18, 19, 20, 21, 22, 23, and 24 illustrate It is obvious, however, that the U-shaped other modifications in the form of the U- 45 piece might be severed at its base orthe base shaped piece. Fig. 25 shows in side elevaremoved, so thatabreak in the magnetic cirtion, and Fig. 26 in edge View, a modification cuit formed by the iron mass would then exist of my invention. V at two points, at one or both of which the va- In Figs. 1 and 2 G G 0 indicate a conductriable closure mightbe produced in the manor of copper or other material, with binding 5 ner to be hereinafter described. The numposts or clamps B, B for receiving ends of circuit-wires on which instrument is placed. Current is passed from B to B, or the reverse, and traverses the conductor in a circular path, as shown, the parallel portions of the conductor being separated by a layer of insulation.

P P indicate agate or ruby pivots for the needle-shaft, which carries the horseshoe or U-shaped piece of iron I, as shown. The pivots P P are not in the center of the circular part of O C C, but are to the left and up ward, as shown. A counter-weight W and the needle or pointer N serve together to so nearly counterbalance the weight of I and its supports that the resultant center of gravity will be situated so as to cause the needle to come to rest with the parts I IV N about in the position shown in Fig. 1, N pointing to the zero of the divided scale S.

A level L may be used to assist in adj usting the level of the instrument.

The part C C O can be cast with the scale S and lugs to carry the pivots P P all in one piece of copper, or it may be built up of parts. The exact relation of the axis between P P to the curved circular portion of C O C is of considerable importance to the proper work ing of the instrument. While in the figure the external part of G C is shown as extended bya spiral web starting at D and ending at E, this is not essential, but the part of G O 0 around the axis could be made of a circular band without the web. The spiral web D E is of considerably less thickness than the circular part of O C 0 possesses. There is also a slight depression or concave spot in C O C, near the point D and to the left of the piece I when the needle is at zero, as shown.

The reduction or contraction mentioned and the spiral web from D to E are added to insure by the depression at 'D the movement of the needle under small currents and to Fig. 1. i If current passes in C, magnetism de-.

veloped in I tends to close its magnetic circuit around 0 externally, as indicated by dotted lines, Fig. 4, representing lines of magnetic force joining the ends of the horseshoemagnet I. The parts in Fig. 4 will tend to move to position Fig. 3, in order that I may better close its magnetic circuit external to C, or in order that the magnetism developed in I may better conform to the circular magnetism developed around 0 by the current passing in it; but, as in Fig. 1 the part I is hung at P P, the movement from the position Fig. 4 to that Fig. 3 can only be accomplished by a swing to the left, which moves the pointer N to the right over the scaleS and raises the combined center of gravity of N, WV, and I by rotating it to the left and upward.

The effect of the spiral or expanding web which begins at D, Fig. 1, and extends around O O O, widening at the same time, is to give to give deflections proportional to the cur-. I

rentinstead of deflections in a higher ratio, as will be the case when such web or its equivalentis not used. The manner of its action is exemplified in Fig. 5. Since the whole section of C is traversed by the current, and web F is a part of that section, the passage of the magnetic lines from the ends of I over the exterior of Owill be in part hindered by the current in F tending to force the lines to pass out around it. The ends of I are, as shown, preferably bent outward.

In Fig. 6 the form of O in section is such as to be the equivalent of O F, Fig. 5, and in Fig. 7 the section of C is again modified by addition of a smaller conductor F outside C, but at a varying distance from it. Thus in Fig. 8 D F shows this modification as a separate smaller band around 0, placed spirally thereto, or thereabout.

Where it is necessary to have several turns in C, it can either be cast in duplicated sections and connected in series, or it may be a coil of wire 0 0, Figs. 9 and 10, in which the index is pivoted eccentrically, as at P. In such a case the best form of coil to use is not a circular one, but one which departs from a circular outline by having a slightly flattened or contracted place at D to correspond to the depression near D, Fig. 1, and which in passing around to the left from I) widens from the circular outline indicated by the inner dotted circle, but which does not, however, pass out to the limit of the outer dotted circle, or that described by the ends of the piece I, Fig. 1, which overhang the coil 0. Indeed, the ends of I should as the needle turns on its pivot P continually increase the overhang of the extremities of I, but at a rate only proportional to the increase of deflecting-power of the current. It is often, however, convenient to have thercoil possess nearly or quite a circular form, as when used for voltmeter or potential indicators, and wound with comparatively fine wire. In such case the pivot P, Fig. 12, or center upon which the indicator turns, may be displaced or made eccentric to the coil one-sixth of the internal diameter, or one-third of the radius. In such case the practicable range of movement of the iron U-shaped piece or horseshoe will be from radius P a to P b.

I prefer to use the instrument, as shown in Fig. 13, connected with mains M M, the po tential between which is to be determined.

To avoid the necessity of winding coil 0 with very fine wire and to eliminate eifects of increase of temperature in its coils, I place it in series with other resistances, as of German silver, or, better, of incandescent lamps G G G one or morewhich resistances or lamps, as used, are run hot and form by far the larger as to maintain them at a temperature'far su-a perior to that of the air around, and are not therefore affected by air-temperature. The use of incandescent lamps gives another advantage. They may be so chosen that for given volts between M and M they shall be heated. to such a point (low redness) that their resistances are critical or subject to fall on slight increase ofcurrent, or rise on decrease of current, due to changes in potential between M and M. This gives greatlyenhanced sensitiveness to" the indications: of N I, because of thechanges so occuring. Thus, if for one hundred (100) voltsin dicator N stands at 100 on the scale, a very small increase of volts will increase the current from M M through G, &c., and lower tential readings the instrument may be furthcr improved by duplication of the coil 0 and part I, as in Figs. 14 and 15. Here two coils O C and O O'are so placed that one is' in front of the other, but displaced, so that the indicator-axis is eccentric to one C by being on the left of its center and eccentric to the other 0' by being on the right of its center. The iron pieces I I are carried opposite and nearly or' quite balance each other."

Small counter-weights, adjustable, if needed,

are provided to govern the position of the center of gravity of the system and cause the indicator to stand at zero when I I are in the positions shown similar to that in Figs. 1 and 13. Where the two coils O 0 thus act conj ointly, greater sensitiveness and positiveness are secured. The form of the piece I may be greatly modified. In the preceding figures it has been considered as a fiat bar of iron bent as shown in Figs. 16 and 17. It could be divided into several pieces or cut through the middle into two parts, but would be less sensitive.

as indicated by dotted lines, Fig. 18, or tapered edgewise, as in Fig. 19, or rounded, as in Fig. 20, or notched or serrated, as in Fig. 21. The bend at d, Fig. 22, may be an angle, or, as shown, a portion of a curve or circle. The bar itself may be round, square, or rectangular, or other section, a rounded bar being shown in Figs. 23 and 24, with the ends 6 e tapered out and flattened. The section of the conductor or coil 0 may be square, round, or of other shape.

It is not essential that the pivot P for the index be eccentric to the coil 0 when equiva-' lent conditions are existing for movement of the U-piece I; but when such equivalent con Instead of turning the ends c c outward they could be thinned or tapered,

ditions are not provided the pivot should be eccentric. a a

In Figs. 25 and 26 the axis at P is concentric with coil 0, and bar I hangs suspended therefrom, as shown. In such case no move ment of I would take place on current passing in the coil C; but if a bent plate or curved surface of iron H H be placed outside the "coil, in a position somewhat spiral thereto, the ends of I can,by moving to the leftin Fig. 25, gradually approachthe piece 11 H,

which may act as a keeper therefor. By suitably bending or shaping H H so as to secure various rates of approach of I to it, as the turning on its pivot takes place, any desired properties may be given to the instrument,

such that the readings may be proportional to the current in G,o r'may be less or more In this case coir than proportional to it. ductor C and mass I might obviously be secured together and move as one; or, byshap ing H H properly places of superior sensitiveness to slight changes of current in C' may be produced, or the reverse. This is done by slightly changing the form of the surface of II H presented to I, so that the rate of approach of theends of I toward HE is increased or diminished for'agiven' range of movement of the pointer N over the scale S. I do not limit myself to the special'form's l of apparatus hereinbefore described, since the principle of my invention may be embod- IOO ied in other constructions. 7

hat I claim as my invention is 1. The combination, with an electric conductor carrying an electric current, of a mass of iron partially embracing said conduct-or and adapted to form through its whole range of movement from zero a partial magnetic circuit around the same and movable in the: general longitudinal direction of the conductor' to positions where it will gradually efiect a change in the degree of closure of the IIO magnetic field arbund the conductor, as and for the purpose described. 2. The conductor 0, having its mass at one side modified or varied, as described, in comj bination with an armature adapted to partially close the magnetic circuit around said conductor, as and forthe purposeset forth.

3. The combination, with an electric conductor, of a U-shaped armature or its equiv alent, as described, mounted at the end of a pivoted arm and movable bodily in the general longitudinal direction of the conductor, a

as described, to positions where it may effect a variable closure of the magnetic circuit" around the conductor, as set forth.

4:. The combination of a conductor and an armature which normally partially embraces and closes the magnetic circuit around the 5. The combination, substantially for the purpose described, of an electric conductor and a U shaped armature partially surrounding the conductor and mounted, as described, on the end of a pivoted arm so as to have a movement of translation bodily over the conductor in the general direction of the axis of the same.

6. The combination, with the electric conductor, of a mass of iron partly encircling the same constantly or through its whole range of movement, said conductor and mass of iron being movable bodily with relation to one another, as described, in the general direction of the conductors longitudinal axis, but at a slight angle, so that the conductor may be gradually included more and more Within the iron, as and for the purpose described.

7. The combination, with two coils or conductors placed one beside the other, but eccentrically, of the two armatures or magnet-closing pieces, one for each coil, mounted upon a movable support or its equivalent, as described, and adapted to move in the general plane of the coils or conductors.

8. The combination, with the two conductors C, of the two armatures partially encircling the same in the zero position and mounted upon a common support in proper manner to balance one another.

9. The combination, with the curved conductor C, of the index and connected armature forming an iron mass partially surrounding the conductor and mounted on an arm pivoted eccentrically to such curved conductor, said armature consisting of one or more pieces of iron which normally or in the zero position of the apparatus overlap upon the sides of the conductor, as and for the purpose described.

10. The combination of the armature and the conductor 0, having its mass near the open side of the armature, or just in advance of the same, reduced or contracted, as and for the purpose described.

11. The conductor O, having on its outer side a Web of varying depth, in combination With the armature Whose magnetic circuit is closed across or around said Web.

12rThe combination, With an electrore 

